In multi-component seismic detection and exploration, seismic waves are the target waves which indicate the structure and attribute of the earth. In general, the seismic waves comprise two independent seismic sections of the primary wave (P-wave) and the shear wave (S-wave) and commonly follow ray paths refracted by the varying density and modulus (stiffness) of the Earth's interior. In low-velocity zone of earth mantle, P-waves are often considered to be received by the vertical components and S-waves by the horizontal components.
However, real data records, P-wave and S-wave vectors are polar linearly in general, show that it is not true and precise in many areas with relatively high-velocity zone, and such phenomenon known as “mode leakage”. In other words, there is potential cross-contamination of P-wave energy on the horizontal components and S-wave energy on the vertical components. Therefore, suppression of mode leakage, namely wave separation (separation of P- and S-waves), become a critical aspect and difficult issue for the multi-component seismic data processing.
Conventionally, there are two major groups of methods for P and S-wave separation. One group is the scalar-processing method using a domain transformation, such as the f-k method or the Tao-p method. The other group is the vector-processing method that separate different wave motions and recover their amplitudes based on the polarization characteristics, such as the direct mapping method or the polarization method.
Expressions for wavefield separation have previously been derived by for instance Dankbaar, J. W. M., 1985, Separation of P- and S-waves: Geophys. Prosp., 33, 970-986 (hereinafter referred to as the Dankbaar), and these have been applied to seismic data in conventional recording geometries.
In CN patent application entitled “System and method for seismic wavefield separation” (CN Patent Publication No. CN1404582A, hereinafter referred to as the 582 application.) The 582 application applies filtering technique in the spatial domain to convert vertical spatial derivatives to horizontal derivatives and calculate all spatial derivatives of the wavefield based on the wavefield separation of Dankbaar. In addition, the 582 application resolves some drawbacks of Dankbaar, such as use limitations of low/dropping velocity zone of the near-surface, and adjusts error occurred for wavefield separation in anisotropic near-surface.
In CN patent application entitled “Method for synthesizing X and Z component wave field vector” (CN Patent Publication No. CN101251603A, hereinafter referred to as the 603 application.) The 603 application applies wave velocity analysis method to project two components for wave separation. Such projection neglects important features of three-component of explored seismic datum, and results in poor amplitude preservation, improper migration and low imaging resolution, especially to some areas contained the mode leakage with complex structures or thinnish low/dropping velocity zone.
In CN patent application entitled “Method for separating seismic wave fields of different types in two-dimensional vertical seismic profile” (CN Patent Publication No. CN101630017A, hereinafter referred to as the 017 application.) The 017 application separates the waves by using an inverse transformation from VSP data under a coordinate system for three-component seismic array data. However, the 017 failed to recover amplitudes of separated waves after separating using the inverse transformation method, which can not effective provide the full amplitudes of separated waves.
Accordingly, although above mentioned patent applications may realize the wave separation, the applications failed to recover the true amplitudes for vectors of separated waves. Because of the mode leakage phenomenon, the waveforms left after suppression of the mode leakage generally are not the actual true amplitudes. The cross-contamination of P-wave energy on the horizontal components and S-wave energy on the vertical components are becoming the partially projected waves.
Therefore, there is a need for an approach to provide a mechanism that can adapt to the wave separation of a seismic wave with suppressed mode leakage and generates separated P-wave and S-wave with true amplitudes.